Conventional transportation requires fuels that burn cleanly and that have high energy densities for efficient storage at ambient conditions. These criteria are currently met by petroleum-derived, liquid fuels (e.g., gasoline, diesel, kerosene). Petroleum is a non-renewable resource in diminishing supply, with large quantities of the known supply located in politically unstable regions of the world. Additionally, the combustion of fossil fuels to generate kinetic energy leads to emission of CO2. Carbon dioxide is a greenhouse gas that contributes to global warming. See Klass, “Biomass for Renewable Energy, Fuels, and Chemicals,” Academic Press, San Diego, 1998. The ecological, economical, and political issues associated with the continued reliance on petroleum-based fuels would be ameliorated (at least in part) by producing clean-burning liquid fuels from renewable biomass resources. There is a general consensus in the scientific community that the amount of biomass that could be grown globally on a sustainable basis is comparable to the annual world-wide consumption of energy by the transportation sector. Perlack et al. 1-78, United States Department of Energy, Oak Ridge National Laboratory, 2005.
The cost of transportation fuels produced from ligno-cellulosic biomass, however, is currently not competitive with the cost of fuels derived from petroleum. This is due primarily to the high costs associated with the processing of biomass to produce the fuel, rather than the cost of the biomass feedstock itself. See Hamelinck et al., “Production of FT transportation fuels from biomass; technical options, process analysis and optimisation, and development potential,” Energy 29, 1743-1771 (2004). Accordingly, it is imperative to develop new processes for converting biomass to liquid fuels that involve a limited number of processing steps. Limiting the number of processing steps decreases the capital and operating expenses associated with conventional processes that require multiple reactors and separation/purification steps between reactors.